In the recently growing market for mobile devices, such as mobile phones, PDAs, the diversity in functionalities has increased so that in most existing mobile devices a display is provided having a cursor which can be controlled by the user usually by means of a joystick which may contain, for example, five switches arranged in conjunction with a knob to be operated by the user for obtaining the movement of the cursor on the display. The respective switches are closed depending upon the movement of the knob of the joystick to the left or right side or for obtaining the “click” function by moving (depressing) the joystick vertically, when a menu on the display has been reached and the cursor for selecting a predetermined item is actually positioned.
For easy operation of the mobile devices a continuous and highly sensitive and reliable control of the cursor by means of the joystick is required, and the joystick must be compact, robust and must have a high performance in conjunction with a low price.
In this connection, reference WO 2007/122556 A2 discloses a detection circuit for detecting the movements of a movable object, such as a joystick, wherein a plurality of first detection units is provided for detecting the presence or absence of a light spot on the detection units, the light spot being influenced in its position by the movement of the movable object according to the user's intention (the operation by the user). Second detection units are provided for detecting light intensities of the light spot depending upon a movement of the movable object in a further direction. Specifically, two intensities of the light spot are detected by the second detection units, and a corresponding output signal is obtained indicative of the movement of the movable object in a Z direction (vertical movement, representing the click function of the joystick). The output signals of the detection units are compared with corresponding reference signals, and the result is obtained as a one bit digital signal. The signals are digitalized at every photodetector of the detection units to obtain the digitalized signal ready for further data evaluation. The detection units comprise photodiodes and transistors for digitizing the signals from the photodiodes.